The present invention generally relates to a system and a method for line-conducted digital communication and, in particular, relates to one such system wherein the connection between the exchange of a telecommunication network and subscribers thereof includes an optical transmission line.
Conventional copper cables in telecommunication networks are being replaced in ever increasing measure by optical cables with waveguides, hereafter called "LWL". These replacements first started with the trunk network. The replacements thereafter expanded to the local exchange network. The declared goal of such replacements was the use of glass fibers as the transmission medium for optical signals in the subscriber station area, thus in the service line network, and to connect it as much as possible to every subscriber, i.e., the so called "fiber to the home". The glass fibers are designed to provide the subscribers with the high signal transmission rates that are possible with this transmission medium. The separate connection lines that were previously required for the different services can now be replaced by a single glass fiber connection. Today such services include, among others, telephone, telefax, telex, teletex, IDN and ISDN (basic and primary multiplex connections). The provision of such a service line network requires suitable devices, particularly for the subscribers, and cost-effective glass fiber transmission systems.
For example, one such known service line network is generally referred to as "Opal". In such a service line network, a select group of subscribers is connected by glass fibers, or LWL, to a local exchange. Glass fibers lead from the exchange to a passive optical distributor, from which the glass fibers extend to five subscribers and a cable branch. The passive service line network divides the light output according to the number of subscribers. Such a system inherently limits the number of subscribers that can be connected to the system. Further, appropriate lasers must be used for light wavelengths of 1330 nm or 1550 nm, for example. Because of the passive distributor, the range of the transmission and the transmission rates are severely limited.
Consequently, it is highly desirable to provide a telecommunication system that is not subject to such limitations.